I need to drive a DC motor with PWM, through a H-bridge.

The controller can't generate PWM at ultrasonic frequencies with resolution I desire, and the low-end of the spectrum (~100Hz) may be too slow for my needs (plus still create a 'hum').

There's a question about driving a fan and the answers suggest 1-4.7uF ceramic + some 100-1000uF electrolytic caps at the output as solution (plus a fast diode to clear reverse current). This works well for a fan, which only turns in one direction. In my case, the motor will operate in both directions, so I can't depend on fixed polarity of the output - the moment I reverse polarity the cap will be fried.

How do I go about silencing the motor in this case?